Lets see if I can help a bit;
Answer 1: Sorry the tell you, but on the schematic you referenced, there was a ground wire shown. The wire between the remote and the + wire is the ground wire. And yes you can connect this to the frame of you're car. The frame of your car is (or should be!) connected the the negative terminal of your battery under the hood somewhere.
Answer 2: The remote wire requires a +12V bias to turn the power supply on. You can hook this up to a +12V switched signal (like off you're ignition). But if you have a swith already on you're +12V source you might as well tie the remote and the +12V lines you have together.
Answer 3: As far as the Orange wire goes. It's a Power Good signal. If you're current motherboard doesn't use it then you should be able to run just fine without it.
Hope this helps...
[ 09-22-2001: Message edited by: littlej ]